1. Field of the Invention
This invention relates to a system for operating a vehicle hood and, more particularly, to a system which can distinguish a collision of a vehicle carrying the system with an object to be protected (e.g., a pedestrian) from a collision of the vehicle with any other object for operating a hood of the vehicle.
2. Description of the Related Art
As a vehicle hood operating system of that type, there is known a hood airbag sensor system as disclosed in, e.g., Japanese Patent Laid-Open Publication No. HEI-8-216826. The known hood operating system has a bumper sensor installed on the front bumper of a vehicle for detecting a substantially horizontal front load and a hood sensor installed above the front portion of a hood for detecting a substantially vertical downward load. If the vehicle collides with an object to be protected, the bumper sensor responds, and the object striking against the hood produces a downward load acting upon the hood sensor, whereby the hood airbag is actuated. If the vehicle collides with an obstacle like a building, however, the hood airbag is not actuated, since no vertical downward load acts upon the hood sensor to place it in operation.
The hood operating system as described does, however, not allow the hood airbag to be actuated until a vertical downward force is produced when the obstacle is an object to be protected, though it may make it possible to avoid any unnecessary outputting of a signal for actuating the hood airbag when the obstacle is, e.g., a building. As a result, the actuation of the hood airbag is delayed. Moreover, it is likely that the hood airbag may be actuated even when an object which is not an object to be protected, but which is lighter in weight, has produced a vertical force by striking against the front bumper.
It is therefore an object of the present invention to provide a vehicle hood operating system which can operate a vehicle hood quickly, while making a judgment of higher accuracy as to any obstacle.
According to a first aspect of this invention, there is provided a vehicle hood operating system comprising: a velocity sensor for detecting a velocity of a vehicle, an acceleration sensor for detecting acceleration caused by an external force directed from a front to a back of the vehicle to to act upon a bumper; a calculation unit for calculating a bumper deformation speed by converting the acceleration detected by the acceleration sensor to a speed, an actuator for lifting a hood a predetermined amount; and a control unit for controlling the actuator such that the actuator lifts the hood when the vehicle velocity detected by the velocity sensor has exceeded a predetermined threshold value, while at the same time, the bumper deformation speed calculated by the calculation unit has exceeded a threshold value varying with the vehicle velocity.
When the vehicle has collided with an obstacle, the system according to the first aspect of this invention can distinguish between two kinds of obstacles accurately in a short time after the collision, since it relies for their distinction upon the bumper deformation speed differing markedly between when the obstacle is an object to be protected, and when it is another object of lighter weight. The bumper deformation speed is high when the obstacle is an object to be protected, but is low when it is another object of lighter weight. If the vehicle has a low velocity not exceeding a predetermined value when it has collided with an obstacle, the actuator is not operated, since there is no high possibility of any secondary collision.
Preferably, the system further includes a memory storing a map containing the threshold value of the bumper deformation speed varying with the vehicle velocity. The threshold value of the bumper deformation speed in the map so varies as to increase with an increase of the vehicle velocity, thereby enabling an accurate distinction of obstacles despite the bumper deformation speed varying with the vehicle velocity prevailing at the time of collision.
According to a second aspect of the present invention, there is provided a vehicle hood operating system comprising: a velocity sensor for detecting a velocity of a vehicle, an acceleration sensor for detecting acceleration caused by an external force directed from a front to a back of the vehicle to act upon a bumper; a first calculation unit for calculating a bumper deformation speed by converting the acceleration detected by the acceleration sensor to a speed; a second calculation unit for calculating an amount of bumper deformation from the bumper deformation speed calculated by the first calculation unit; an actuator for lifting the hood a predetermined amount; and a control unit for controlling the actuator such that the actuator lifts the hood when the vehicle velocity detected by the velocity sensor has exceeded a predetermined threshold value, while at the same time, the amount of bumper deformation calculated by the second calculation unit has exceeded a threshold value varying with the vehicle velocity.
Being thus arranged, the system can distinguish accurately between an obstacle of light weight and an object to be protected, since the amount of bumper deformation caused by the collision of the vehicle with any obstacle is small when the obstacle is an object of light weight, but is large if it is an object to be protected.
Desirably, the system further includes a memory storing a map containing the threshold value of the amount of bumper deformation varying with the vehicle velocity. The threshold value of the bumper deformation amount in the map so varies as to increase with an increase of the vehicle velocity, thereby enabling an accurate distinction of obstacles despite the amount of bumper deformation varying with the vehicle speed prevailing at the time of collision.
According to a third aspect of the present invention, there is provided a vehicle hood operating system comprising: a velocity sensor for detecting a velocity of a vehicle; an acceleration sensor for detecting acceleration caused by an external force directed from a front to a back of the vehicle to act upon a bumper; a first calculation unit for calculating a bumper deformation speed by converting the acceleration detected by the acceleration sensor to a speed; a second calculation unit for calculating an amount of bumper deformation from the bumper deformation speed calculated by the first calculation unit; an actuator for lifting a hood a predetermined amount; and a control unit for controlling the actuator such that the actuator lifts the hood when the vehicle velocity detected by the velocity sensor has exceeded a predetermined threshold value, while at the same time, the bumper deformation speed calculated by the first calculation unit has exceeded a threshold value varying with the vehicle velocity and the amount of bumper deformation calculated by the second calculation unit has exceeded a threshold value varying with the vehicle velocity.
The system thus-arranged ensures a still higher accuracy of obstacle distinction than the system according to the first or second aspect of this invention, as it relies upon both of the speed and amount of bumper deformation for obstacle distinction.
It is desirable that the system further includes a first memory storing a map containing the threshold value of the bumper deformation speed varying with the vehicle velocity, and a second memory storing a map containing the threshold value of the amount of bumper deformation varying with the vehicle velocity. The threshold value in the map of the first memory so varies as to increase with an increase of the vehicle speed. The threshold value in the map of the second memory also so varies as to increase with an increase of the vehicle speed.
According to a fourth aspect of this invention, there is provided a vehicle hood operating system comprising: a velocity sensor for detecting a velocity of a vehicle; a first acceleration sensor for detecting acceleration caused by an external force directed from a front to a back of the vehicle to act upon a bumper; a second acceleration sensor for detecting acceleration caused by an external force directed from a front to a back of the vehicle to act upon a vehicle body; a calculation unit for calculating deceleration acting upon the vehicle body from the acceleration detected by the second acceleration sensor; a timer designed to start counting time when the acceleration acting upon the bumper has reached a predetermined level; an actuator for lifting a hood a predetermined amount; and a control unit for controlling the actuator such that the actuator lifts the hood when the vehicle velocity detected by the velocity sensor has exceeded a predetermined threshold value, while at the same time, the deceleration of the vehicle body calculated by the calculation unit does not exceed a predetermined threshold value, but a predetermined period of time varying with the vehicle velocity has elapsed after the start of the timer.
The thus-arranged system can quickly distinguish between when the obstacle with which the vehicle has collided is a building, and when it is an object to be protected, since it relies upon the deceleration of the vehicle body for judgment as to the nature of the collision.
In a preferred form, the system further includes a memory storing a map containing the length of the predetermined period of time varying with the vehicle velocity. The predetermined period of time in the map so varies as to decrease with an increase of the vehicle velocity. Thus, the system makes proper judgment at any vehicle velocity and ensures an improved accuracy of distinction between a building and an object to be protected.